1. Field of the Invention
The present invention relates to a fabrication method for an optical transmission channel board, an optical transmission channel board, a board with built-in optical transmission channel, a fabrication method for a board with built-in optical transmission channel, and a data processing apparatus.
2. Related Art of the Invention
With recent progress in optical communications and optical information processing, optical circuit mounting technology permitting high-density and economical integration of optical components is increasingly important, and so is the role that optical modules play. An example of a prior art optical module is shown in FIG. 50 (see JP-A-H8-78657).
As shown in FIG. 50, a prior art optical module 1000 comprises a Si substrate (Si terrace) 1101, optical fibers 1102, and a semiconductor laser (optical element) 1105. Guide grooves (V grooves) 1104 a formed in the Si substrate 1101. Each optical fiber 1102 is fixed along each guide groove 1104. Electric wirings 1106 and positioning reference planes (positioning markers) 1103a, 1103b, and 1103c are formed in the Si substrate 1101. Using these positioning reference planes 1103a, 1103b, and 1103c, the semiconductor laser 1105 is mounted on the Si substrate 1101, and connected to the electric wirings 1106. That is, in the optical module 1000, the optical fibers 1102 and the semiconductor laser (LD) 1105 are integrated on the Si substrate 1101. This module is driven through the electric wirings 1106. In the configuration shown in FIG. 50, the guide grooves 1104 can be fabricated with sufficient accuracy on the basis of the good workability of the Si substrate 1101. This permits easy integration of the optical fibers 1102 with the optical element such as the semiconductor laser (LD) 1105 and a photo detector (PD).
FIG. 51 shows another optical module 2000 in which an optical waveguide 1126 in place of an optical fiber is formed on a Si substrate 1101 (see JP-A-H8-78657).
In the optical module 2000 shown in FIG. 51, the optical waveguide 1126 formed on the Si substrate 1101 is optically connected to an opto-semiconductor element 1127 mounted via solder bumps 1128 in a recess formed on the Si substrate 1101.
The mounting hierarchy in a communication system apparatus 3000 for performing optical communications is described below with reference to FIG. 52. The communication system apparatus 3000 shown in FIG. 52 is constructed according to a method called bookshelf mounting. This method has an advantage in economical efficiency and packaging density, and hence is used generally.
Further description is given below.
A component of the communication system apparatus 3000 is a semiconductor element (LSI chip) 130. A plurality of semiconductor elements 130 are used and constitute an MCM (multi-chip module) 1131. The MCM 1131 is mounted on a board (printed circuit board) 1133, so that a board assembly is obtained. A plurality of board assemblies are accommodated in a sub-rack 1135. A plurality of sub-racks 1135 are accommodated in a cabinet 1137, so that the communication system apparatus 3000 is constructed.
The mounting hierarchy of bookshelf mounting is classified into six levels. That is, level 0 indicates a distance within a chip (˜1 mm). Level 1 indicates a distance between chips (˜1 cm). Level 2 indicates a distance within a board (˜10 cm). Level 3 indicates a distance within a sub-rack (˜1 m). Level 4 indicates a distance between sub-racks (˜10 m). Level 5 indicates a distance between apparatuses or systems (˜100 m) (each quantity between parentheses indicates a transmission distance). Among these levels, in the range of transmission distance exceeding 1 m (level 3, level 4, or higher), optical fibers have an advantage as a transmission medium. Thus, the combination of an optical module (such as one shown in FIG. 50) and an optical fiber is used advantageously. In contrast, transmission within a board (level 2) is performed generally using a copper circuit pattern on the printed circuit board. That is, such transmission is performed using electricity, not using light.
On the other hand, JP-A-2000-340907 discloses a wiring board (printed circuit board) that has built-in optical fibers. The wiring board disclosed in JP-A-2000-340907 is shown in FIGS. 53, 54(a), and 54(b).
The wiring board 4000 shown in FIG. 53 comprises an insulating board 1201. The insulating board 1201 is composed of a plurality of insulating layers 1202. Wiring circuit layers 1203 are formed on the insulating layers 1202. Wiring circuit layers 1203 located on different layers are connected through via hole conductors 1204. Optical waveguide bodies 1205 having a fiber shape (such as optical fibers) are embedded in an insulating layer 1202a selected from a plurality of the insulating layers.
As shown in the plan view of FIG. 54(a), the optical waveguide bodies 1205 having a fiber shape are embedded inside an insulating board 1201, so that an optical waveguide circuit is constructed in which optical signals can be transmitted through these optical waveguide bodies 1205. FIG. 54(b) is a sectional view taken along line X-X′ in FIG. 54(a). The inside of the insulating board 1201 of FIG. 54(a) is illustrated as a schematic diagram for general description purpose, and is not necessarily in agreement with the sectional view of FIG. 53.
As shown in FIGS. 54(a) and 54(b), an optical connector 1206 is integrally attached to an end of the optical waveguide circuit in one side of the insulating board 1201. Optical-to-electric signal conversion elements 1207 capable of converting an optical signal into an electric signal is attached in the inside or side portions of the insulating board 1201. Electric signals converted from the optical signals by the optical-to-electric signal conversion elements 1207 are electrically transferred through the wiring circuit layers 1208 (corresponding to the wiring circuits 1203 shown in FIG. 53) and the via hole conductors 1204 arranged inside the insulating board 1201, to an electronic element or the electric connector 1209 mounted on the insulating board 1201.
JP-A-2000-66034 discloses an optical wiring board permitting the wiring of a large number of optical fibers.
The optical wiring board disclosed in JP-A-2000-66034 is shown in FIG. 55. In the optical wiring board 5000 of FIG. 55, one or two or more optical fibers 1311 are mounted on the board using the technique of a picture drawn with a single stroke of a pencil. In the optical wiring board 5000, the optical fibers 1311 are stacked in a certain part.
The optical wiring board 5000 shown in the figure has a four-layer structure. The optical fibers 1311 are arranged on boards 1312 and 1312′. End portions 1313 of the optical fibers 1311 are arranged in line on the same plane, while end portions 1314 are multi-layered.
When an optical module such as the optical module 1000 shown in FIG. 50 is to be fabricated, in a prior art fabrication method, the electric wirings 1106 are fabricated on the board 1101 by etching or the like, and then the guide grooves 1104 are fabricated by machining or the like. As such, the fabrication processes for the electric wirings 1106 and for the guide grooves 1104 are completely separated. This has caused complicated fabrication processes, and hence caused an increase in time and cost.
Further, at a glance of the optical module 1000 of FIG. 50, the module might seem to be fabricated easily. Nevertheless, in practice, centering is necessary between each of the optical fibers 1102 and the optical element 1105. This centering process is notably complicated. The “centering” described here indicates the process of aligning the optical axes of each optical transmission channel (optical fiber) and the optical element (such as semiconductor laser).
For example, when the optical fibers 1102 are single-mode fibers, only a discrepancy in the submicron order is allowable between each optical fiber 1102 and the optical element 1105. Nevertheless, considering the deviation (tolerance) occurring in the fabrication of the guide grooves (V grooves) 104 in the Si substrate 101 and the deviation (tolerance) occurring in the fabrication of the optical element positioning reference planes 1103a, 1103b, and 1103c formed together with the electric wirings 1106, it is concluded that the mounting of the optical element 1105 merely based on the alignment with the optical element positioning reference planes 1103a, 1103b, and 1103c is insufficient because the discrepancy can exceed the tolerance between each optical fiber 1102 and the optical element 1105. Thus, the centering is unavoidable.
Also in the configuration of FIG. 51, electric wirings (not shown) located under the solder bumps 1128 are fabricated in a separate process from that for the optical waveguide 1126. Thus, a similar problem a rises concerning the discrepancy between the optical fiber 1102 and the optical element 1105.
Even if the problem of discrepancy between the optical fiber 1102 and the optical element 1105 could not arise in the optical module 2000 shown in FIG. 51, a higher cost is caused in the fabrication of the optical waveguide 1126 on the Si substrate 1101 in comparison with the case that an optical fiber 1102 is used. Thus, another problem arises concerning economical efficiency.
From the perspective of economical efficiency, the use of copper circuit patterns of a printed circuit board is advantageous, for example, in the within-the-board transmission (level 2) in the communication system apparatus 3000 shown in FIG. 52. Nevertheless, this causes a problem that the upper limit is reduced in the transmission speed. This is because despite that GHz-level transmission is achieved in optical interconnection, merely MHz-level transmission is achieved in electric interconnection.
Further, in the wiring board 4000 shown in FIGS. 53 and 54, centering is necessary between each optical waveguide body 1205 embedded in the insulating board 1201 and each optical-to-electric signal conversion element 1207. This centering process is complicated, and hence increases the cost.
Furthermore, in the within-the-board transmission in the communication system apparatus 3000 shown in FIG. 52, if the electric interconnection were replaced with optical interconnection in order that the problem of transmission speed could be resolved, an unacceptably large number of optical fibers or optical waveguides would need to be arranged on the board. Thus, another problem would arise concerning the actual device structure. More specifically, the board surface would be filled with optical fibers or the like. This causes a difficulty in the handling, as well as an increase in the board size and in the rate of failure such as disconnection in the optical fibers or the like.
Thus, in order that a large number of optical fibers or optical transmission channels should be arranged with in a limited region, the optical fibers or the optical transmission channels could be constructed in multi-stage. Nevertheless, the method for this multi-stage construction is a difficult problem to be devised in the case of the actual configuration of the optical modules 1000 and 2000 shown in FIGS. 50 and 51. A new way of thinking is necessary for solving this problem. That is, in the optical module 1000 shown in FIG. 50, the guide grooves (V grooves) 1104 are formed in the Si substrate 1101 so that the optical fibers 1102 are fixed in the guide grooves 1104. Thus, the configuration of single-stage arrangement is unavoidable in principle. On the other hand, in the optical module 2000 shown in FIG. 51, the optical waveguide 1126 is formed on the Si substrate 1101. Thus, similarly, the configuration of single-stage arrangement is unavoidable in principle.
Further, the wiring board 4000 shown in FIGS. 53 and 54 is disclosed in the case that a single insulating layer 1202a is used and that the optical waveguide bodies 1205 are embedded therein. In contrast, if a plurality of such layers were to be provided in the configuration, a new problem would arise in the method of attaching the optical-to-electric signal conversion elements 1207. In addition, JP-A-2000-340907 does not disclose the case that the optical waveguide bodies 1205 presently embedded in the insulating board 1201 are arranged in a different hierarchy from that of the optical-to-electric signal conversion elements 1207. Accordingly, no disclosure or indication is provided concerning the method for precisely adjusting their positions for their optical connection. Further, although the optical wiring board 5000 shown in FIG. 55 is a board with built-in optical fibers, no disclosure or indication is provided concerning the configuration that optical-to-electric signal conversion elements 1207 are attached directly to all the optical fibers of the optical wiring board 5000. Thus, it should be notably difficult to precisely adjust the positions for optical connection.
With considering the above-mentioned problems in the prior art, a purpose of the present invention is to provide: a fabrication method for an optical transmission channel board which can be fabricated in a simpler fabrication process; such an optical transmission channel board; and a data processing apparatus employing this optical transmission channel board. Another purpose of the present invention is to provide a fabrication method for an optical transmission channel board which needs no centering process or merely a simpler centering process; such an optical transmission channel board; and a data processing apparatus employing this optical transmission channel board.
Yet another purpose of the present invention is to provide a fabrication method for an optical transmission channel board which can be fabricated at a lower cost.
Another purpose of the present invention is to provide a board with built-in optical transmission channel on which an optical element (such as a semiconductor laser) can be mounted, and on which a large number of optical transmission channels (such as optical fibers) can be mounted efficiently. At the same time, a purpose of the present invention is to provide a data processing apparatus employing such a board with built-in optical transmission channel and a fabrication method for such a board with built-in optical transmission channel.